Metal working lubrication has been accomplished, as is well known, by the use of mineral and/or fatty oils. In the early technology, these fats and oils were used alone, but with the advent of improved technology, it was useful to prepare aqueous emulsions of mineral and/or fatty oils in order to reduce costs, improve cooling capacity, and give generally better performance. Until recent years almost all water containing lubricants were emulsions of fatty and/or mineral oils which might or might not contain various additives for particular applications. However, emulsion type products have several inherent problems, as, for example, emulsion stability, and for this reason and others they often find their utility limited. In recent years, water containing lubricants of the solution type have become available and in areas where cooling ability is the primary consideration the water soluble lubricant has shown great merit. However, where conditions require both a high degree of cooling plus a high degree of hydrodynamic or oil film lubricity characteristics, the water soluble lubricants have not been suitable because they have been unable to deposit a film containing sufficient lubricity for proper function under hydrodynamic conditions.
Metalworking fluids are employed in metalworking operations such as cutting, forming, stamping and rolling to provide cooling and lubrication to both the workpiece and the metalworking apparatus. The metalworking fluids also function to flush away oil and debris from the worksite, and they provide corrosion protection to both the workpiece and the metalworking apparatus. Initially, metalworking fluids comprised oil-based materials or emulsions of water and oil. However, the industry has increasingly sought to replace oil-based products with water-based materials. Therefore, the industry is turning toward the use of water-based metalworking fluids.
In addition to providing a cooling function, water-based metalworking fluids must provide good lubricity to the workpiece and metalworking apparatus, and be capable of sequestering and removing debris and contaminants, including oils, from the worksite. In addition, water-based metalworking fluids should provide good corrosion protection to both equipment and workpieces. Toward that end, the industry has developed various water-based metalworking fluid compositions; however, a number of problems have arisen in connection with the use of such compositions.
Metal working processes of many kinds are used in the fabrication of metal goods. Typically metal is removed from the work-piece during metal working. Examples of metal working processes include machining, cutting, drilling, grinding, turning, milling, tapping and broaching. Metal working differs from metal forming. In metal forming typically no metal is removed. Examples of metal forming processes include rolling, forging, molding, stamping, casting, ironing, drawing, and extruding. In metal forming operations, the metal is typically preheated to at least about 800° C. so that the metal can be more easily formed into the desired shape. In metal working operations, the metal is typically not preheated; the only heat incident to the operation is that caused by the metal working operation itself.
In all metal working operations it is necessary to lubricate the interface between the workpiece and the tool to decrease the force required to work the metal; to cool the work-piece; to remove chips from the cutting zone; to impart a good surface finish; and to extend the life of the tool. The formulation of lubricant compositions is complex, because a wide variety of compounds may be used, as, for example, antifriction agents, anticorrosion agents, surfactants, and biocides.
Triaryl phosphate esters have been proposed in the past for use in metal working lubricant compositions. Berens, U.S. Pat. No. 4,362,634, discloses metal working lubricant compositions that comprise a polyol ester, such as a pentaerythritol/fatty ester, as the major ingredient together with a triaryl phosphate ester and a carboxylic ester non-ionic surfactant of the anhydrosorbitol or glycerol ester type, such as sorbitan monotallate. The phosphate ester comprises 1 to 10 weight % of the concentrated lubricant composition. About 2 to 30 weight % of concentrated composition can be dispersed with water to form a diluted lubricant composition as an emulsion that was reported to be phase stable for at least one hour under quiescent conditions.
Historically, metalworking lubricant formulations are made by combining several separate ingredients that are known, individually, to have lubricating functions. For example, various oils, block copolymers, liquid crystal formers and surface active agents would be coupled together and provided to the final users as blended products.
Metal working lubricant compositions are preferably produced as concentrates, which are diluted prior to use. Concentrated lubricant compositions are prepared by the manufacturer and shipped in drums to the user, who may store the drums of concentrated lubricant composition for several weeks to months prior to use. Because the lubricant properties of the metal working lubricant composition are typically lost if the lubricant composition deemulsifies, the concentrated lubricant composition should have a shelf life (stability, i.e., time before deemulsification occurs) at room temperature (about 25° C.) of at least one month, and preferably at least six months. The high temperature (about 75° C.) stability and the low temperature stability (about −15° C.) should each be at least 5 days. Following dilution of the concentrated lubricant composition, the resulting diluted lubricant composition should have a shelf life at room temperature of at least one month, preferably at least six months, a high temperature stability of at least one day and a low temperature stability of at least one day.
It is also known that metalworking lubricants based on natural fats and oils (triglycerides) have been used in the art and utilized throughout the industry for a variety of processes including rolling, stamping, drawing, pickling, cutting and extruding. Aqueous formulations of natural fats and oils are widely used as the rolling oil in the cold rolling of steel to provide lubrication and cool the rolls.
In addition to providing effective lubrication and effective cooling of the workpiece/working elements, there are other criteria which must be met by metalworking lubricants. Rolling oils, for example, must be capable of providing a continuous coating on the surface of the metal. Furthermore, this coating or film must have a minimum thickness and must be substantive enough to the metal so that it will be maintained at the high pressures which occur in the roll bite. Above and beyond these lubrication considerations it is particularly advantageous if the rolling oil provides some measure of corrosion protection to the rolled strip and burns off cleanly during the annealing operation. Most cold rolled strip is annealed by heating at about 1300° F. in a reducing atmosphere to relieve internal stresses built up during the prior working operations and to give the finished steel the desired physical properties. Residual rolling oil must volatilize cleanly and should not leave any carbonaceous deposits or surface discoloration.
In view of variations in the metals being worked and the different operating conditions and application methods employed, numerous metalworking oils based on natural fats and oils have been developed in an attempt to obtain the optimum balance of properties. Most of these variations have involved the use of different fats and oils or replacement of a portion of the fat or oil with a petroleum product, e.g. mineral oil, or a synthetic lubricant, e.g. a synthetic hydrocarbon or ester. Emulsifier systems have also been widely varied and additives have been employed to enhance the characteristics of these oils.
To a lesser extent the natural fats and oils have been chemically modified to alter their properties. U.S. Pat. No. 3,202,607 discloses the ethoxylation of castor oil and their use in aqueous dispersions for metalworking. In British Pat. No. 847,517 two moles triglyceride and one mole polyethylene glycol are interesterified to produce useful products which are mixtures of mono-, di-, and triglycerides and mono- and diesters of polyethylene glycol. Products useful for resolving water-in-oil emulsions which are the reaction product of castor oil with a polyalkylene glycol and an organic dicarboxy acid, such as diglycolic acid or phthalic anhydride, are disclosed in U.S. Pat. No. 2,925,429. U.S. Pat. No. 2,971,923 discloses similar products for breaking petroleum emulsions and desalting mineral oils.
U.S. Pat. No. 3,720,695 discloses ester lubricants which have a wide variety of uses obtained by first transesterifying castor oil with polyoxyethylene glycol of molecular weight greater than 1000, and then, in a separate and distinct step, esterifying the available hydroxyl groups with a mono- or dicarboxylic acid.
Mixed ester products having significantly improved water solubility are disclosed in U.S. Pat. Nos. 3,634,245 and 3,928,401. The mixed esters are obtained by reacting a triglyceride with a short-chain mono- or dicarboxylic acid and a low molecular weight polyoxyethylene glycol in a single-step operation. Mixed ester products which are readily emulsifiable with water and useful as metalworking fluids, obtained by treating a triglyceride under transesterification conditions with a polyoxyalkylene glycol and a high molecular weight dicarboxylic acid, such as a polymeric fatty acid, are disclosed in U.S. Pat. No. 4,067,817. Blends of the mixed ester with hydrocarbon oils, e.g. mineral oil, are described in U.S. Pat. No. 4,108,785.
Whereas numerous metalworking lubricants based on both unmodified and modified triglycerides have been developed, there is a continuing need for new products. This is particularly so where the new products present economic advantages and/or performance advantages. Performance advantages can include greater latitude in the ability to effectively formulate the lubricant. It can also include improvement in one or more of the properties of the lubricant. It is particularly effective if these improvements are achieved without adversely affecting the other essential properties of the lubricant.
There is also a need in the art for both concentrated and diluted metal working lubricant compositions/emulsions that are stable for longer periods so that they can be produced and stored for longer periods of time prior use.